What is Disease?

What is Disease?
What is Disease?

A disease is a particular abnormal condition that negatively affects the structure or function of part or all of an organism, and that is not due to any external injury. Diseases are often construed as medical conditions that are associated with specific symptoms and signs. A disease may be caused by external factors such as pathogens or by internal dysfunctions. 

Diseases can affect people not only physically, but also mentally, as contracting and living with a disease can alter the affected person’s perspective on life.

There are four main types of disease: 

  1. infectious diseases 
  2. deficiency diseases 
  3. hereditary diseases
  4. physiological diseases

The deadliest diseases in humans are coronary artery disease (blood flow obstruction), followed by cerebrovascular disease and lower respiratory infections. In developed countries, the diseases that cause the most sickness overall are neuropsychiatric conditions, such as depression and anxiety

The study of disease is called pathology, which includes the study of etiology, or cause.

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In many cases, terms such as disease, disorder, morbidity, sickness, and illness are used interchangeably. There are situations, however, when specific terms are considered preferable.


The term disease broadly refers to any condition that impairs the normal functioning of the body. For this reason, diseases are associated with dysfunctioning of the body’s normal homeostatic processes.

Acquired disease

An acquired disease is one that began at some point during one’s lifetime, as opposed to disease that was already present at birth, which is a congenital disease. Acquired sounds like it could mean “caught via contagion”, but it simply means acquired sometime after birth. 

Acute disease

An acute disease is one of a short-term nature (acute).

Chronic condition or chronic disease

Chronic disease is one that persists over time, often characterized as at least six months but may also include illnesses that are expected to last for the entirety of one’s natural life.

Congenital disorder or congenital disease

A congenital disorder is one that is present at birth. It is often a genetic disease or disorder and can be inherited.

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Genetic disease

A genetic disorder or disease is caused by one or more genetic mutations.

Hereditary or inherited disease

A hereditary disease is a type of genetic disease caused by genetic mutations that are hereditary (and can run in families)

Iatrogenic disease

An iatrogenic disease or condition is one that is caused by medical intervention, whether as a side effect of a treatment or as an inadvertent outcome.

Idiopathic disease

An idiopathic disease has an unknown cause or source. As medical science has advanced, many diseases with entirely unknown causes have had some aspects of their sources explained and therefore shed their idiopathic status.

Incurable disease

A disease that cannot be cured. Incurable diseases are not necessarily terminal diseases, and sometimes a disease’s symptoms can be treated sufficiently for the disease to have little or no impact on the quality of life.

Primary disease

A primary disease is a disease that is due to a root cause of illness, as opposed to secondary disease, which is a sequela, or complication that is caused by the primary disease.

Secondary disease

A secondary disease is a disease that is a sequela or complication of a prior, causal disease, which is referred to as the primary disease or simply the underlying cause (root cause).

Terminal disease

A terminal disease is one that is expected to have the inevitable result of death. Previously, AIDS was a terminal disease; it is now incurable, but can be managed indefinitely using medications.


The terms Illness and sickness are both generally used as synonyms for the disease. However, the term illness is occasionally used to refer specifically to the patient’s personal experience of his or her disease.


A disorder is a functional abnormality or disturbance. Medical disorders can be categorized into mental disorders, physical disorders, genetic disorders, emotional and behavioural disorders, and functional disorders. 

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This blog provides general information and discussions about health and related subjects. The information and other content provided in this blog, or in any linked materials, are not intended and should not be construed as medical advice, nor is the information a substitute for professional medical expertise or treatment. If you or any other person has a medical concern, you should consult with your health care provider or seek other professional medical treatment. Never disregard professional medical advice or delay in seeking it because of something that has read on this blog or in any linked materials. If you think you may have a medical emergency, call your doctor or emergency services immediately.

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